Asteroid hurtles past, thrilling scientists and doing no harm

The largest asteroid to pass close to Earth in decades hurtled by Tuesday afternoon, appearing as only a faint streaking glow on your average telescope but lighting up NASA’s powerful radar screens.

The 1,300-foot-wide asteroid came within roughly 201,000 miles of the planet, within the moon’s orbit. Posing no threat to Earth, it allowed NASA scientists at the Deep Space Network antenna in the Mojave Desert their closest peek ever at such a massive space rock.

The radar images were detailed enough to allow NASA’s Jet Propulsion Laboratory, based in La Cañada Flintridge, to create a short video of the spinning asteroid as it approached.

“The animation reveals a number of puzzling structures on the surface that we don’t yet understand. To date, we’ve seen less than one half of the surface, so we expect more surprises,” said radar astronomer Lance Benner, the lead scientist on the project.

NASA blasted the asteroid with microwaves from a radio telescope near Barstow, using the 230-foot-wide aluminum dish to receive signals bouncing off the asteroid. That data revealed its ridges, craters and boulders and provided enough information about its speed, trajectory and physical characteristics to allow JPL officials to plot its course for the next 64 years.

Benner said the data show that the asteroid, named 2005 YU55, will have another close encounter with Earth in 2075. It will skim close to Venus in 2029.

Its proximity gives researchers a rare opportunity to study the physical characteristics of a massive asteroid, adding to the research and understanding of bodies floating in space and offering a glimpse, perhaps, of the forces that created the universe, Benner said.

Robert S. McMillan, the University of Arizona scientist who discovered the asteroid, said the orbits, size, shape and mechanical structures of these “near-Earth objects” provide clues to their origins and may help explain how they escape the asteroid belt between Mars and Jupiter.

“We know the orbit extremely well,” McMillan said while appearing on a webcast on Slooh.com, which provided live pictures of the asteroid Tuesday from its telescope in the Canary Islands. “We know it’s not going to hit the Earth.”

McMillan, head of the university’s Spacewatch Project to track near-Earth objects, warned that scientists will have to keep an eye on the asteroid because its course after 2075 cannot be determined reliably, even with all the new research.

McMillan discovered the asteroid in December 2005 while conducting a routine survey of space searching for asteroids. This one, YU55, jumped out because of its unusual path and rapid speed, he said.

“We detect thousands of asteroids in any clear night, but one in a thousand has a motion different from those in the main asteroid belt between the orbits of Mars and Jupiter,” he said.

NASA has identified more than 8,000 near-Earth asteroids, including more than 400 that are at least half a mile wide. Thus far, none is classified as a threat.

phil.willon@latimes.com